1. Field of the Invention
This invention relates to lacquers and more particularly to lacquers useful for coating plastic surfaces.
2. Art Background
The refurbishing of telephones is a significant problem for communication companies. When a telephone is returned from a user location scratches and other surface defects are present. Typically, before these marred telephones can be relocated with a new user, the defects must be eliminated. In this case, the surface defects are remedied by spraying the telephone with a lacquer. The polymer used in the lacquer and which ultimately forms the coating on the telephone significantly affects the physical properties of the telephone. For example, if the added polymer coating develops a crack, this crack often initiates a crack in the adjacent telephone body. Thus, even though the telephone body itself might initially be more resistant to impact than the added polymer, its impact resistance after refurbishing is that of the coating polymer.
The properties of the coating polymer are also significant when recycling of the original telephone body is contemplated. When a telephone body has been damaged so that lacquering is not a suitable alternative, the plastic is usually salvaged by recycling. For telephones previously treated with a lacquer, the polymer coating will be incorporated into the recycled plastic. Often these incorporated coatings cause a degradation in the impact resistance of the basic polymer. This degradation phenomenon again is a substantial problem when the recycled plastic is employed in molded bodies, which are subject to frequent abuse.
Even if a polymer is found which does not degrade the impact properties of the treated plastic, it is often quite difficult to devise an acceptable lacquer based on this polymer. A lacquer, for commercial use, must satisfy certain prerequisites. For example, as discussed, the solid components of the lacquer, i.e., the component which ultimately remains on the coated body, must not degrade the properties of the coated plastic. The polymer must also disperse sufficient added pigment to yield sufficient hiding power for adequate coverage of the coated body. Typically, the hiding power of the lacquer increases linearly with the amount of pigment deposited. Since the pigment is dispersed through intermolecular interactions with the polymer solids portion of the lacquer, the amount of pigment deposited in turn depends on the concentration of the polymer in the solvent component of the lacquer. This interdependence of hiding power and solubility introduces a requisite of the solvent component of the lacquer. That is, the solvent component must be chosen so that, in view of the inherent hiding power of the solid component, sufficient polymer and thus pigment is dispersed to produce the desired opacity.
Besides satisfying the limits imposed by hiding power, the solvent component must also conform to pollution control standards. For example, California statutes strictly limit the solvents which may be used commercially. Such enviornmental considerations make lacquer formulation much more difficult.
The lacquer, as a combination of the individual solid and solvent components, also must have certain attributes. The viscosity must be sufficiently low to allow the lacquer to be easily sprayed and sufficiently high to prevent formation of runs on the coated surface. Additionally, the lacquer must evaporate at a rate which precludes webbing, and, the formation of an orange peel type of agglomeration surface. These defects typically occur when the solvent evaporates too rapidly.
The gloss of the coating and the permanence of the coating are also important properties. The lacquer must dry to a shiny finish which adheres to the coated surface. If a poorly formulated lacquer is used a low gloss or nonadherent coating is often the result.
The necessity for maintaining impact strength and the difficulties associated with lacquer formulation has retarded development of suitable lacquers for telephone refurbishing.